\begin{tabular}{l*{3}c}
\hline\hline
 & (1) & (2) & (3) \\
\hline
pop\_int&259660&478080&-218420\\
&[158372]&[897326]&(163593)\\
\hline
Observations & 18 & 32 & 50 \\
\hline\hline
\end{tabular}
